Duplex xerographic reproduction apparatus



DUPLEX XEROGRAPHIC REPRODUCTION APPARATUS April 14, 19 70 c. F. CARLSON 3 Sheets-Sheet 1 Original Filed. Jan. 5, 1964 uumwaom Z zEbm INVENTOR. CHESTER F. CARLSON ATTORNEY April-14, 1970 c. F. CA'RLSON 3,50 ,347

DUPLEX XEROGRAFHIC REPRODUCTION APPARATUS Original Filed Jan. 5, 1964 5 Shets-Sheet 2 INVENTOR. CHESTER F. CARLSON ATTORNfY April 14, 1970 c. F. CARLSON 3,506,347

' DUPLEX XEROGRAPHIC REPRODUCTION APPARATUS Original Filed Jan. 5, 1964 3 Sheets-Sheet 3 INVENTOR. CHESTER F. CARLSONV United States Patent O assignments to Xerox Corporation, Rochester, N.Y., a-

corporation of New York Continuation of application Ser. No. 335,536, Jan. 3, 1964. This application Oct. 19, 1967, Ser. No. 676,653

Int. Cl. G03g 15/22 US. Cl. 3553 20 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus for forming xerographic reproductions on both sides of a copy sheet in which a first tackifiable xerographic powder image is formed on a support, the powder image on the support is subjected to solvent vapors rendering the powder image tackified, the tackified image is transferred to the first side of a copy sheet, a second tackifiable xerographic powder image is formed on the support, the powder image on the support is subjected to solvent vapors rendering the powder image tackified, and the second tackified image is transferred to the second side of the copy sheet.

BACKGROUND OF THE INVENTION This application is a continuation of application Ser. No. 335,536, filed Jan. 3, 1964.

This invention relates to xerography and more particularly, it releates to novel method and apparatus for forming xerographic reproductions on both sides of a support sheet.

In the process of xerography, for example, as disclosed in Carlson Patent No. 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising a layer of photoconductive insulating material on a conductive backing is given a uniform electric charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional projection techniques. This exposure discharges the plate areas in accordance with the radiation intensity that reaches them, and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with electrostatically charged, finely-divided material such as an electroscopic powder that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed xerographic image is usually transferred to a support surface to which it may be fixed by any suitable means.

In recent years there has been a growing use of xerography in automatic drum-type machines for producing full size copies from microfilm intermediates or from full-size originals, as shown, for example, in Johanson US. 3,049,968 and Cerasani et al. US. 3,076,392.

Xerography has become a valuable new tool, not only for producing copies of documents and engineering drawings, but also for reproducing entire books. Many out-ofprint books have thus again been made available. It has also been possible for libraries and individuals to replace badly deteriorated books with bound xerographic copies on good paper. Xerography has also made possible the publication of limited editions of theses, legal briefs, and other papers, where the size of the edition is so small that its publication by conventional printing methods would be prohibitive, or at least unduly burdensome.

In the xerographic reproduction of books as practiced at the present time, it is customary to first produce a microfihn copy with the pages copied preferably side by ice side in sequence on a continuous strip or reel of film. The film is then fed through an automatic xerographic drumtype machine where the pages are enlarged to full size and the resulting xerographic powder images are applied in sequence to one side of a web of paper upon which they are then aflixed by heat fusing. After removal of a length of the paper web carrying a series of images on one side representing a sequence of papers, the web is fan-folded, bound along one edge and a cover applied to produce a completed book. Each leaf of the book, therefore, has two thicknesses of paper joined by a fold at the free edge and bound at the back so that the reader, in turning a page, finds text printed on both exposed sides. The unprinted side of the paper is enclosed within the fold and is hidden from view, but nonetheless the physical bulk of the book is twice greater than it would be if both sides of the paper could be used. Therefore, despite the success of the xerographic process, it has heretofore been used in a manner in which a reproduction is formed on only one side of a support sheet. Irrespective of whether the original or originals being reproduced contain reproducible information on both sides, as is the case with many opaque originals, or otherwise lend themselves to a feasible duplex reproduction, it has heretofore been the practice to reproduce each copy face essentially on a separate single reproduction sheet. It should be readily apparent, therefore, that current practice, particularly with multiple page documents, produces twice the bulk and consequently twice the paper consumption as compared to What can be realized by duplex reproduction.

The need for duplex copying from both a practical and economic point of view has, therefore, been long recognized. Despite the long felt need, it has heretofore encountered handicaps which were unable to be resolved. First, the fusing step as conventionally performed utilizing heat or a solvent vapor causes the powder image to become soft and tackified which in the past has caused the always present problem of offsetting and smudging particularly where both sides of the sheet were subjected to heat or vapor simultaneously. Second, where sequential transfer was attempted to opposite sides of a sheet, long time delays were required to assure complete fusing of the first side before attempting transfer to the second side. Alternatively, complicated scheduling was required for subsequent interspersing of the various pages. Thirdly, as is known, heat fusing causes crinkling as well as drying of the paper support sheet, such that it is difficult to get uniform contact for a subsequent electrostatic transfer step While at the same time imposing a fire hazard by subjecting the already dried paper to a subsequent heat fusing step. Thus, these prior handicaps have prevented the emergence thereof on a commercial scale.

SUMMARY OF THE INVENTION Now in accordance with the instant invention, there is provided novel method and apparatus by which duplex xerographic copying can be readily and simply achieved. Accordingly, it is an object of the invention to provide novel method and apparatus for effecting duplex xerographic reproduction.

This and other objects as well as the various features, advantages and limitations of the invention will become apparent from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic sectional elevation of an apparatus for performing the method in accordance with a first embodiment of the invention;

FIG. 2 is a detail of a program timer comprising part of the apparatus of FIG. 1;

FIG. 3 illustrates a modification of the image transfer station in the embodiment of FIG. 1; and

FIG. 4 illustrates a modification of the copy sheet exposure station in the embodiment of IfIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, an automatic drum-type xerographic machine is shown, according to one aspect of the invention, for producing two-sided xerographic copies. The images are produced in sequence for the two sides of any two-sided original or from the single side of two separate originals so that, for example, page 2 is produced and transferred to side 2 of a copy sheet immediately after page 1 has been applied to the first side. This is accomplished without danger of smudging or undesired olfsetting, with no substantial time delays, and no thermal deterioration of the copy paper. Moreover, since the images are applied in sequence, no complicated scheduling is required.

The machine is shown arranged to produce full-size copies enlarged from the frames of a reel of microfilm on which have previously been recorded a sequence of images in side by side relation, such as microcopies of the succeeding pages of a book. It is contemplated, however, that other exposure sources can be substituted. For example, an optical system can be used for copying from full-size original sheets, in the manner illustrated, for example, in Eichler et a1. U.S. Patent 2,945,434. In this event it will be necessary for an operator to place the originals, one after another, on the exposure copyboard during operation in a manner whereby the left margin of the original will be reproduced as the top of the copy sheet as will be understood. It is also contemplated that the exposure position can be occupied by the phosphor screen of a cathode ray tube upon which are displayed facsimile images or characters received over a transmission channel from a distant source, froma computer, or the like.

The xerographic drum 11 in this embodiment and its associated charging, exposure development, cleaning and discharging devices may be of types known in the art, and is shown, by way of illustration, as an adaptation of the machine disclosed in Eichler et al. U.S. Patent 2,945,434.

Instead of providing for direct transfer of the powder images from the xerographic drum to copy sheets, however, a transfer drum 12 is provided, to which the powder image is transferred, and upon which it is softened or tackified by application of solvent vapor, after which pressure transfer is effected to the final copy sheets. While the transfer drum is shown of the same diameter as the xerographic drum, it may be either larger or smaller than the xerographic drum, provided the drive. mechanism is arranged to drive them both at the same peripheral speed and that the copy sheet feeding mechanism is synchronized to feed copy paper to the transfer drum at the appropriate point in the operating cycle to place the transferred images in the desired positions on the copy sheets.

In the machine of FIG. 1, the operative components are mounted in a light-tight cabinet 13 which includes means for shielding the xerographic drum from room light and in which all the operative components are contained. Microfilm 10 to be copied is fed from a supply reel 14 to a take up reel 15, in an optical slit projection system, generally similar to that shown, for example, in Johanson U.S. Patent 3,049,968.

Light projected through the microfilm passes through a shielded light passage 20 and a 45 degree mirror 23 to the xerographic drum 11. The emulsion side of the microfilm is positioned in the projector so as to yield a rightreading electrostatic image on the xerographic drum surface, rather than the mirror-reversed image usually required where direct transfer is made from drum to copy paper. The microfilm is advanced intermittently as by an instant-start and stop synchronous motor (not shown) controlled by a program timer 24 (FIG. 2). The timer also controls the paper feeding mechanism designated 25 for the copy paper 26, which is to receive the final xerographic images. The drive rollers are adapted in this embodiment to move a microfilm frame at a constant rate across the projection zone and then stop for a brief period before advancing the next succeeding frame. Indexing marks or holes can be provided in the microfilm and sensing means arranged to cooperate therewith in a well-known manner to ensure accurate registration of the individual frames.

Xerographic drum 11 includes an accurately machined metal cylindrical member coated uniformly on its periphery with a uniform layer of photoconductive insulating material, such as vitreous selenium, or other such material useful in xerography, and is mounted on shaft 29 in suitable bearings in the frame of the machine. The drum is driven in a counter-clockwise direction by a motor 30 at a constant rate that is proportional to the projection rate of the copy, whereby the peripheral rate of the drum surface is identical to the projection rate of the reflected light image. The drum surface comprising the layer of photoconductive material on a conductive backing is sensitized prior to exposure by means of a corona generating device 31, Which may be an adaptation of the type disclosed in Vyverberg Patent No. 2,965,756 and which is energized from a suitable high potential source.

The exposure of the drum to the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the light image projected from the copy. As the drum surface continues its movement, the electrostatic latent image passes through a developing station 40 in which a two-component developing material 41, which may be of the type disclosed in Walkup Patent No. 2,638,416, is cascaded over the drum surface by means of a developing apparatus 42. i

In the developing apparatus, developing material 41 is carried up by conveyor 43 driven by suitable drive means from motor 30- and released onto chute 44 wherefrom it cascades down over the drum surface effecting development of the latent image thereon. Toner component 45 of the developer that is consumed in developing 1s stored in dispenser 46 and is released in amounts as controlled by the dispenser mechanism. Other types of development could be employed including well-known forms of powder cloud, brush, liquid, magnetic, etc.

After development, the powder image passes through the first image transfer station or position 50 at which point transfer drum 12 rolls lightly in contact with the gnlaige to effect transfer under the influence of an electric After transfer, the xerographic drum surface passes through a cleaning station 56 at which the surface is brushed by a cleaning brush assembly 57 rotated by motor 30, whereby residual developing material remaining on the drum surface is removed. The powder removed from the drum surface is exhausted through port 58 by means of suction provided from fan 59 where it becomes lodged in a removable filterbag 67. Thereafter, the drum surface passes through a discharge station 68 at which it is illuminated by a fluorescent lamp 69 whereby the drum surface in this region is completely flooded with light to remove any electrostatic charge that may remain thereon. Suitable light traps are provided in the system to prevent any light rays from reaching the drum surface other than the projected image, during the period of drum travel immediately prior to sensitization by corona generating device 31 until after the drum surface is completely passed through developing station 40.

Transfer drum 12 may be comprised of an accurately machined metal drum 51 which is covered or coated with a non-conducting abhesive material 52. Material 52 is characterized in that it does not readily or effectively form a mechanical bond to sticky materials, and more particularly to the powder developing material when supported thereon after transfer, either in a dry or tackified state, as will be understood, but readily permits the powder material to be temporarily held thereon electrostatically.

The abhesive material layer 52 may comprise a tetrafiuoroethylene polymer resin, or a fluorinated copolymer of ethylene and propylene, such materials being available commercially as Teflon resin finishes and sheets. The layer may be applied as a finish to the cleaned and primed steel drum by spray, dip or brush coating, followed by drying and heat fusing. Teflon sheet material may alternatively be cemented to the drum surface, since such films are available with one surface which is cementable.

In order to further enhance the abhesive character of the layer it is preferred that the Teflon surface be coated with a silicone oil, which is also an abhesive-type material. One such suitable oil is Dow Corning 200 silicone fluid, 100 cs. viscosity at 25 C. The silicone can be applied by wiping the surface with a porous cloth or paper saturated with the fluid, and the coating can be maintained in operation by using a cleaning web of porous paper or cloth which has been pre-treated with silicone.

Preferably layer 52 particularly where intended for recycling use, should also be substantially non-absorbent of solvent vapors as will be understood. Other materials that have relatively little affinity for developing material, such as silicone coated baked enamel, bonded glass layers or closely woven glass fiber cloth may also be employed, if desired. Also, although materials having a low bond strength for tackified and/or hardened powder images are considered more practicable for use with the apparatus of the invention, it should be noted that materials having a higher bond strength for powder image material such as paper may also be employed in the form of an expendable web.

Shaft 53 of transfer drum 12 is journaled in bearings 54 which are mounted in insulating blocks 55 attached to the frame of the machine. The drum is connected through contact with one of the bearings with a terminal 60 connected to a potential source of several hundred volts, for instance 300 to 1000 volts, depending upon the thickness of the non-conducting abhesive layer and other factors, in order to create an electrostatic field of attraction for the powder image at the first transfer station.

The xerographic and transfer drums are accurately spaced in relation to each other to provide light pressure contact between the abhesive surface of the transfer drum and the powder image on the xerographic drum at the line of transfer, without producing such heavy pressures that the powder layer 'will be compressed or mechanically bonded to either drum surface. The two drums are synchronously driven at the same peripheral speed.

The potential applied to transfer drum 12 is adapted to maintain the drum at the opposite polarity to the charge on the powder image. If the powder carries a negative charge the drum is biased positively, and vice 'versa. The powder is thereby transferred electrostatically, in mirror-reverse image configuration, to the abhesive surface of transfer drum 12 as it rotates in a clockwise direction.

A vapor fusing chamber 61 is mounted below the transfer drum and comprises a shallow tank 62 with side Walls 63 and 64. The walls are arranged to extend up into closely-spaced relation to the curved drum surface and to extend along parallel to the drum for a short distance, so that the drum substantially closes the top of the vapor chamber, With just sufficient space provided for clearance of the powder image by the side walls of the tank. A bath of liquid solvent 65 for the resin of the powder image, is maintained in the bottom of the tank below the drum surface. Wicks 66 of porous material extend up the side walls to aid in generation-of solvent vapor in the chamber. Any volatile solvent for the resin of the powder image may be used. Typically this includes such materials as trichlorethylene, certain Freons, or hydrocarbon solvents.

As the transfer drum rotates, it carries the powder image through the vapor tank in which the image rapidly becomes tackified or liquified during the time of passage through the chamber. Due to the close spacing of the side walls and the location of the second transfer station designated 70 at the point of emergence of the image from the vapor chamber, there is very little solvent vapor drag-out from the chamber. The images emerge from the chamber in tacky or semi-liquid condition.

At second transfer station 70 a rubber covered transfer roller 71 is mounted to roll against the transfer drum at the point of egress of the drum surface carrying the tackified image from the vapor tank. Operatively associated with transfer roller 71 are paper feed and recycling members, whereby a sheet of copy paper can be fed against the transfer drum by transfer roller 71 to pick off the tackified resin image as it emerges from the vapor tank.

A program timer 24 for controlling the paper feed and recycling means is illustrated in FIG. 2. It comprises a series of earns 79, which may be mounted directly on the xerographic drum shaft 29, or on a shaft geared to the drum. Cam is adapted to open and close an electric switch which controls the microfilm advance mechanism previously described. Cam 81 controls a switch operating an electromagnet to swing paper stop arm 89 to a paper release position. The third, fourth and fifth cams, 92, 93, and 94 respectively, control levers arranged in a wellknown manner to rotate a frame 86 carrying sheet advance roller 87, deflector platen cam 97, and paper feed mechanism 25.

It will be appreciated that there may also 'be provided manual controls to vary the operation of the microfilm advance, and paper feed to take the control away from the program timer during start-up, shut down, or unusual operating conditions.

The paper feed mechanism 25 comprises a paper tray holder 82 in which a stack of blank copy paper 26 is held for dispensing one sheet at a time, as by pusher 84, onto an inclined feed platen 85. A pivoted frame 86 is mounted above the platen and carries a continuously driven sheet advance roller 87, which by action of cam 92, can be rotated down into cooperative relation with an idling roller 88 set in the feed platen. A paper stop arm 89 is mounted on a pivoted shaft 90 close to the transfer roller 71 and an'idling roller 91 rides against the underside of the transfer roller.

The cams, levers, and magnetic members, under control of the program timer, operate in a coordinated manner to activate the paper feed mechanism to advance one copy sheet under sheet advance roller 87, to then move roller 87 down on top of the copy sheet to advance it up the platen into contact with stop arm 89 where it is delayed momentarily until the stop arm releases it. Since the sheet advance roller continues to rotate, the paper will buckle up slightly in the center and maintain pressure of the leading edge against stop arm 89. The stop arm is then released by a slight counter-clockwise rotation of its shaft (as viewed in FIG. 1) under control of the timer, to allow the sheet to be fed around the transfer roller into contact with transfer drum 12, where it is urged against and picks off the vapor-tackified resin image.

Release means, such as an air puffer 95, separates the leading edge of the copy from the transfer drum as it emerges from transfer roller 71, and the sheet passes out between the transfer roller and upper idler roller 83. In two-sided copying, the one-sided copy produced in the first transfer falls again onto feed platen 85 and may slide down into contact with stop abutment 96 at the lower edge of the feed platen, sheet advance roller 87 having been retracted by its pivoted support frame before the copy emerged.

The short time delay introduced between individual microfilm frame exposures is such that at least a small arc of the xerographic drum remains unexposed between images, and since in xerography unexposed large areas do not develop, there remain image-free gaps between individual pages of copy on the transfer drum. As soon as the one-sided copy has dropped onto the feed platen 85 after receiving a first image it is in a position to be fed through the transfer roller again. It will be noted that the copy falls onto the platen with image side uppermost, and hence on the second feeding, the unused back of the sheet is brought into contact with the transfer drum. Under control of the program timer sheet, advance roller 87 and stop 89 are actuated as before to feed the sheet through the transfer roller a second time to receive the next succeeding xerographic image on transfer drum 12 onto its unused side. The solvent is evaporated almost instantly from the copy so there is immediate setting of the image and no danger of Smudging or offsetting.

Before the leading edge of the copy emerges a second time, a deflector platen 101 mounted above and generally parallel with the sheet feed platen is rotated slightly under control of timer-operated cam 97 to bring its upper right-hand end (as viewed in FIG. 1) down (as shown dashed) against transfer roller 71 and in a position to receive the copy sheet as it emerges. The finished two-sided copy thereby slides down under continuously rotating sheet removal roller 102 where it is moved to the left and under sheet-stacking roller 105 which ejects the copy onto finished copy tray 106. By this means the copy paper is changed end for end or side for side by the sheet feeding and transfer mechanism, resulting in a two-sided copy which can be bound into a book. Thus, if the sheets are fed endwise the top of the copy can be bound in. The person reading will then be able to read the second side by mere lifting up the bottom end of the sheet. Where side- Wise feeding is used, the sheets can be bound at the edge in the usual Way. On turning a page the reader will find the left margin of the second side to be at his left as in ordinary books. In other words, the transfer mechanism results in copy properly oriented for binding in the usual way used in the neat binding process for books, or for binding with clasp fasteners at the left edge, or top, as in internal report binding methods.

It will be appreciated that if the operator desires to make single-sided copies, this can readily be done by manually locking cam 97 in a position to hold the deflector platen in operative position. In this event, each single-sided copy is deflected direct to the finished copy tray.

After an image has been transferred to a copy sheet, a very small amount of dried resin toner may remain loosely bonded to the surface of the transfer drum. This is removed by a wiper consisting of a web of soft paper on cloth-like material 107, which is fed from a supply roll 108 to a take-up roll 109 around a soft pressure roll 110 of felt, foam rubber, or other soft material, pressing against the drum above the paper transfer position. In some instances, as described aforesaid, the web may be pre-treated with silicone liquid in order to maintain the silicone coating on the transfer drum.

Since the abhesive coating on the transfer drum is an insulating material, it has a tendency to pick up electrostatic charges during the transfer and cleaning operations which may interfere with subsequent transfer steps. In order to bring the surface to a reference potential the drum surface passes, after cleaning, and before contact with the xerographic drum, under a conductive wiper, such as a cellulose sponge 115 kept moist with pure water. The sponge is supported in a metal channel 116, which is insulated from the frame, but is connected to a conductive part of the transfer drum. Since the abhesive coating is not wettable with water, the surface does not carry away a film of moisture and hence there is substantially no loss of moisture from the sponge.

FIGURE 3 shows schematically another embodiment of the invention in which the xerographic image is tackified directly on the xerographic drum and transfer is made to the copy paper directly from the drum in a manner similar to that described in connection with FIGS. 1 and 2. In this embodiment, the photoconductive insulating material is provided With an albhesive surface treatment or coating. Vitreous selenium, upon which has been spread a thin film of silicone oil, such as Dow Corning 200 silicone fluid, provides such a surface. In the case of other lphotoconductors, a very thin Teflon finish may be applied and then silicone treated. Operation is otherwise similar to that described for FIG. 1.

Referring now to FIG. 4, there is illustrated an exposure system that can be substituted for the microfilm system of FIG. 1. By eliminating the reversing mirror to obtain direct projection, it can also be employed in the embodiment of FIG. 3. For utilization of this embodiment, an original copy sheet here designated is manually inserted by the operator onto a feed platen 121 into the bite of a pair of continuously operative feed rolls 122 and 123 to advance the sheet until engaging a vertically extending stop member 124. The stop member is supported extending from a pivotal arm 127 with its hooked upper edge narrowly clearing the peripheral surface of continuously rotating drum 125 and adapted to trap the leading edge of the sheet. At a time instant, which may be optionally determined by the operator, a solenoid 126 is energized by means of a switch (not shown) causing arm 127 to pivot about axis 128 to lower stop 124 while placing idler roll 129 against the sheet pressed into contact with the rotating drum 125. In this latter position, the original is caused to move with the drum While being guided by spaced guide members 130 and 131. As the sheet advances coincident with drum rotation, it passes an opening 139 formed between the guides whereat on moving therepast, it is illuminated by lamps 140 and 141. This causes the copy image to be optically transmitted through objective lens 144 onto mirror 145 and then downwardly through an exposure slit 146 onto the surface of drum 11.

On emerging from under idler roll 147, the sheet proceeds onto downwardly inclined chute 148 to drop therefrom onto platen 121 in inverted and reversed end-toend relation as compared to the first feeding position. If the second face is to be copied, the operator proceeds as before in order to expose the second face for reproduction. Where only a single face is to be reproduced, the original can be discarded following a single exposure. Where making repeated copies from the same original, the operations can be repeated with the same original, the appropriate number of times by continually refeeding. Accordingly, the operation can be interrupted at any point after a first face, second face or any repeated number of copies have been made.

It should be apparent from the description of this exposure embodiment when considered in conjunction the remaining apparatus of FIG. 1 that since the same relative sequence takes place with the copy paper at the transfer station as occurs in FIG. 4 with exposure, the ultimate copy will be a duplicate of the original in every way. If the originals are one-sided and the copies are to be two-sided, then the operator simply feeds each original once through the exposure position with the first original top first and the second original, bottom first (or both top first if copy is to be different from original end to end).

Whereas this last embodiment has been described as adapted particularly for a manual feed operation, it should be readily apparent that the feeding system can be mechanized and programmed by using a feeding mech anism for exposure which is a duplicate of the copy 9 paper feed mechanism already described in connection with FIG. 1.

By the description above, there has been disclosed a novel and unique method as well as apparatus for achieving duplex xerographic reproduction. Operation is extremely rapid since the vapor softened toner image sets out very rapidly after transfer from the transfer roll to the copy paper, being on the order of a fraction of a second. The method was found to have extremely low solvent consumption since the copy paper is not exposed to vapor and the only absorption of solvent is in the powder image. This also contributes to the high speed of operation since only minor amounts of vapor are required to be absorbed by the powder image being much less than would be needed for fusing the image on the copy paper, since the image need only be brought to a tacky state rather than be completely liquefied. The process accords many advantages among which are the substantial reduction in bulk of printed publications or the like which previously were prepared with a reproduction on only one side of a page. In addition, the process makes it possible to place images on surfaces to which electrostatic transfers cannot conveniently be made such as heavy card stock, metal sheets, etc. At the same time, it has been found that the smooth surface of the abhesive material accords improved electrostatic transfer from the xerographic drum due to more uniform conditions at the point of separation between the smooth surface and that of the drum.

Whereas specific embodiments have been described in disclosing the invention, it is intended that many variations would become readily apparent to one skilled in the art. For example, for reproducing a single copy of a microfilmed publication, a single copy sheet is described being processed on both sides before processing subsequent sheets. For reproducing multiple copies, it might be preferable to operate the apparatus in a manner in which a plurality of sheets are processed on one side only with identical copy before reprocessing to add second identical copy to opposite sides of each sheet. With the microfilm apparatus illustrated in FIG. 1, a backup mechanism would be required in order to advance the same microimage past the exposure plane the required number of times.

Likewise, it should be readily apparent that a twosided original can be reproduced either in the manner described by inverting the original after a first exposure, or by a simultaneous or sequentially arranged exposure of both sides directed to form each image on separate drums adapted to effect sequential transfer to opposite sides of a copy sheet.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for forming xerographic reproductions on first and second sides of a copy sheet including,

means for forming first and second tackifiable xerographic powder images on a support, means for rendering each of said powder images tackified, and

copy advance means for advancing a first sideof the copy sheet on which the reproduction is to be formed into contact with one of said tackified images and for advancing the second side of the copy sheet into contact with the other of said tackified images.

2. Apparatus according to claim 1, said copy advance means including means for sequentially placing first and second sides of a copy sheet in contact with said tackified images.

3. Apparatus for forming xerographic reproductions on first and second sides of a copy sheet including,

abhesive support means on which to support tackifiable xerographic powder images,

means for forming first and second tackifiable xerographic powder images on said abhesive support means,

means for rendering each of said powder images on said abhesive support means tackified,

copy support means for supporting a copy sheet on which reproductions are to be formed,

copy advance means for advancing a copy sheet from said copy support means in a first orientation to contact one of said tackified images,

means for separating a copy sheet with an image thereon from said abhesive support means, and

means for returning a sheet from said abhesive support means to said copy advance means in inverted relationship to said first orientation for advancement into contact with the other of said tackified images.

4. Apparatus according to claim 3 further including,

copy receiving means on which to support a copy sheet,

and

means for optionally discharging a copy sheet from said sheet returning means to said copy receiving means.

5. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

means for forming first and second tackifiable powder images on a xerographic plate member,

abhesive support means on which to support xerographic tackifiable powder images,

means for transferring said first and second tackifiable powder images from said xerographic plate member to said abhesive support means,

means for rendering each of said powder images on said abhesive support means tackified, and

copy advance means for advancing a first side of the copy sheet on which the reproduction is to be formed into contact with one of said tackified images and for advancing the other side of the copy sheet into contact with the other of said tackified images.

6. Apparatus according to claim 5 wherein said copy advance means includes means for placing first and second sides of a copy sheet in contact sequentially with said tackified images.

7. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

means for forming first and second tackifiable powder images on a xerographic plate member,

abhesive support means on which to support xerographic tackifiable powder images,

means for transferring said first and second tackifiable powder images from said xerographic plate member to said abhesive support means,

means for rendering each of said powder images on said abhesive support means tackified,

copy support means for supporting a copy sheet on which reproductions are to be formed,

copy advance means for advancing a copy sheet from said copy support means in a first orientation to contact one of said tackified images,

means for separating a copy sheet with an image thereon from said abhesive support means, and

means for returning a sheet from said abhesive support means to said copy advance means in inverted relationship to said first orientation for advancement into contact with the other of said tackified images.

8. Apparatus according to claim 7 further including,

copy receiving means on which to support a copy sheet,

and

means for optionally discharging a copy sheet to said copy receiving means from said sheet returning means.

9. Apparatus for forming xerographic reproductions on first and second sides of a copy sheet including,

a xerographic plate member having an abhesive overcoating thereon,

means for forming first and second tackifiable powder images on said Xerographic plate member,

means for rendering each of said powder images on said xerographic plate member tackified, and

copy advance means for advancing a first side of the copy sheet on which the reproduction is to be formed into contact With one of said tackified images and for advancing the other side of the copy sheet into contact with the other of said tackified images.

10. Apparatus according to claim 9, said copy advance means including, means for placing opposite sides of a copy Sheet in contact sequentially with said tackified images.

11. Apparatus for forming Xerographic reproductions on first and second sides of a copy sheet including,

a xerographic plate member having an abhesive overcoating thereon,

means for forming first and second tackifia-ble powder images on said xerographic plate member,

means for rendering each of said powder images on said xerographic plate member tackified,

copy support means for supporting a copy sheet on which reproductions are to be formed,

copy advance means for advancing a copy sheet from said copy support means in a first orientation to contact one of said tackified images,

means for separating a copy sheet with an image thereon from said Xerographic plate member, and

means for returning a sheet from said xerographic plate member to said copy advance means in inverted rela tionship to said first orientation for advancement into contact with the other of said tackified images.

12. Apparatus according to claim 11 further including,

copy receiving means on which to support a copy sheet,

and

means for optionally discharging a copy sheet from said sheet returning means to said copy receiving means.

13. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

means to form tackifiable Xerographic powder images of copy containing a solvent soluble component on a support,

solvent generator means to generate a vapor atmosphere of a solvent of said solvent soluble component of the powder images,

means to pass powder images on said support through said atmosphere of solvent vapor to render the powder images tackified,

copy advance means to sequentially advance opposite sides of a copy sheet into contact with different tackified images on said support and separating means to effect removal of a copy sheet from said last recited relation. '14. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

means to form a tackifiable xerographic powder image of copy containing a solvent soluble component on a support,

solvent generator means to generate a vapor atmosphere of a solvent of said solvent soluble component of the powder image,

means to pass a powder image on said support through said atmosphere of solvent vapor to render the powder image tackified,

copy advance means to advance a copy sheet into contact with a tackified image on said support, separating means to effect removal of a copy sheet from said last recited relation, and

means adapted to optionally discharge a copy sheet removed by said separating means into inverted operative relationship with said copy advance means for advancement thereby and to a copy receiving means.

15. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

a xerographic drum supported for rotation,

means to form a tackifiable Xerographic powder image containing a solvent soluble component on said drum,

an endless abhesive material supported to be advanced into moving contact with said drum, transfer means to transfer the powder image from the drum to the surface of said abhesive material,

solvent generator means to generate a vapor atmosphere of a solvent of said solvent solu-ble component of the powder image,

means to advance said abhesive material containing the powder image through said atmosphere of solvent vapor to render the powder image tackified,

means to support a copy sheet on which the reproductions are to be formed,

feed means to sequentially advance first and second sides of a copy sheet from said copy sheet support means into contact with tackified images on said abhesive material,

separating means to elfect removal of the copy sheet from said last recited relation, and

means adapted to discharge a copy sheet removed by said separating means into inverted operative relation with said copy feed means.

16. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

a xerogra-phic drum supported for rotation, said drum comprising a photoconductive insulating material on a conductive substrate and overcoated with a transparent abhesive material,

means to form a tackifiable xerographic powder image containing a solvent soluble component on the surface of said abhesive material,

solvent generator means to generate a vapor of a solvent of said solvent soluble component of the powder image,

means to pass the powder image on said abhesive material through said atmosphere of solvent vapor to render the powder image tackified,

means to support a copy sheet on which the reproductions are to be formed,

feed means to sequentially feed first and second sides of a copy sheet from said copy sheet support means into contact with tackified images on said abhesive material,

separating means to effect removal of a copy sheet from said last recited relation, and

means to discharge a copy sheet remove-d by said separating means into inverted operative relation with said copy feed means. 17. Apparatus according to claim 16 in which said copy sheet discharge means is adapted optionally to discharge a copy sheet to a copy receiving means.

18. Apparatus according to claim 17 in which said copy sheet discharge means comprises a pivotally-hinged deflector plate extending in the vicinity of copy sheet separation and operative in a first position to efiect copy sheet discharge to the copy sheet feed means and operative in a second position to effect copy sheet discharge to a copy receiving means.

19. Apparatus for forming xerographic reproductions on two sides of a copy sheet including,

means to form a tackifiable Xerographic powder image containing a solvent soluble component on the surface of a continuous substantially abhesive support,

solvent generator means to generate a vapor atmosphere of a solvent of the solvent soluble component of the powder image,

means to advance said abhesive support containing the powder image through said atmosphere of solvent vapor to render the powder image tackified,

. tray means to support a stack of cut copy sheets on which the reproductions are to be formed,

first feed means to singly feed individual copy sheets from the stack in said tray,

second feed means adapted to receive individual copy copy discharge means comprises a pivotally-hinged de- 13 14 sheets from said first feed means and feed a copy References Cited sheet into contact with a tackified image on said UNITED STATES PATENTS support, separating means to effect removal of a copy sheet 2,726,166 12/1955 Greaves X from a relation with an image on said support 5 2,990,278 6/1961 Carlson copy receiving means adapted to receive copy sheets 3,013,878 12/1961 Dessauer 961 having two sided reproductions thereon, and 35062410 11/1962 Shepardson et a1 means adapted to effect discharge of a copy sheet 3 213 2/1963 calson having a reproduction on one side into inverted op- 1698 3/1963 Chlldrcss et a1 11717-5 erative relation with said second feed means and 10 3,149,931 9/1964 Gundlach 34-155 to efiect a discharge of a copy sheet having repro- 8/1965 carlscfn 117-21 X ductions on both sides into said copy receiving 32 1 means. 20. Apparatus according to clalm 19 1n whlch sand 15 JOHN MlHoRANmrimary Examiner flector plate extending in the operative vicinity of said U S 01 XR separating means, and means to effect two position opera- 355 17 tion of said plate. 

